This study aims at gaining a more precise insight into the neural and behavioral mechanisms involved in the homeostasis of body fluids. The receptor, effector and integrative actions of the osmoreceptor- supraoptic nuclear complex in the hypothalamus underlie the neuroendocrine, neurovisceral and the neurobehavioral reflexes which are responsible for the constancy of the volume and tonicity of the fluid internal environment. We intend to explore antidromically identified magnocellular neuroendocrine cells in the supraoptic & paraventricular nuclei and in the internuclear zone in the chronically prepared unanesthetized and behaving monkey with extracellular recording techniques and statistical analysis of spike trains in relation to drinking & sleep-waking behavior, sensory (nociceptive) input, conditioning and hibituation, plasma levels of osmolality & vasopressin,arterial blood pressure and blood temperature. In acutely prepared, anesthetized & paralyzed dogs & and monkeys we intend to explore antidromically identified supraoptic neurons with intracellular techniques of recording electrical membrane properties and staining cell soma and processes of these neuroendocrine cells with a fluorescent dye (Procion Yellow, ICI). We intend to examine the effects of electrical brain stimulation and infusions of pharmacological agents on unit activity, plasma levels of osmolality & vasopressin and urine flow in the behaving, unanesthetized monkey. By these three types of experimental approaches we hope to further define the functional and structural characteristics of magnocellular neuroendocrine cells in relation to the motivational state and their role in the homeostasis of body fluids.